Apparatus for aligning and seating the shot cylinder in a metal die casting machine

ABSTRACT

A hot chamber metal die casting machine is disclosed in which the shot cylinder and gooseneck seat are constructed of dissimilar materials which have substantially different thermal characteristics. Means are provided which Vertically align the shot cylinder in the gooseneck seat and which hold the lower end of the cylinder in sealing contact with the gooseneck seat during the shot-making operation. Another means is provided for vertically aligning the shot piston in the shot cylinder. Additional means are provided for disengaging the shot cylinder from the gooseneck seat at the end of a production period before the gooseneck seat is allowed to cool down. The various alignment, hold-down and disengagement means automatically compensate for the differential in expansion which occurs between the shot cylinder and gooseneck seat and thereby greatly improve the casting operation.

United States Patent [191 Bennett APPARATUS FOR ALIGNING AND SEATING THE SHOT CYLINDER IN A METAL DIE CASTING MACHINE [75 Inventor: Foster C. Bennett, Columbus, Ohio [73] Assignee: The Dow Chemical Company,

Midland, Mich.

[22] Filed: June 28, 1972 [21] Appl. No.: 267,085

Related US. Application Data [63] Continuation-impart of Ser. No. 116,915, Feb. 19,

1971, abandoned.

1451 Apr. 17, 1973 Primary Examiner-Robert D. Baldwin Att0rneyWilliam M. Yates et al.

[ ABSTRACT A hot chamber metal die casting machine is disclosed in which the shot cylinder and gooseneck seat are constructed of dissimilar materials which have substantially different thermal characteristics. Means are provided which Vertically align the shot cylinder in the gooseneck seat and which hold the lower end of the cylinder in sealing contact with the gooseneck seat during the shot-making operation. Another means is provided for vertically aligning the shot piston in the shot cylinder. Additional means are provided for disengaging the shot cylinder from die gooseneck seat at the end of a production period before the gooseneck seat is allowed to cool down. The various alignment, hold-down and disengagement means automatically compensate for the differential in expansion which occurs between the shot cylinder and gooseneck seat and therebygreatly improve the casting operation.

7 Claims, 3 Drawing Figures APPARATUS FOR ALIGNING AND SEATING THE SHOT CYLINDER IN A METAL DIE CASTING MACHINE CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of U. S. application Ser. No. 116,915, filed Feb. 19, 1971, now abandoned.

BACKGROUND OF THE INVENTION The invention relates generally to die casting of metals. More specifically, the invention covers an improved apparatus for aligning and seating the shot cylinder in a hot chamber metal die casting machine.

In a hot chamber metal die casting machine the injection or shot cylinder usually comprises a metal sleeve or liner which is threaded or press-fitted into the gooseneck. To make a metal shot, a piston moves down in the cylinder to force molten metal out of the cylinder and into-the gooseneck outlet bore. The function of the shot cylinder, therefore, is to provide a pressure chamber and guide sleeve for the shot piston. In this capacity the shot cylinder must have good wear re sistance, high strength at operating temperature, and it must be sealed in the gooseneck.

To provide a shot cylinder which will meet these requirements is a particular problem in the die casting of certain metals, such as alloys of magnesium and aluminum. For example, in addition to high strength and good wear resistance, the shot cylinder material must be capable of resisting high temperatures and chemical attack from the aluminum constituent in these metal alloys. Materials which will withstand the molten metal.

environment in the casting machine usually have relatively low coefficients of thermal expansion. The gooseneck structure on the other hand, is usually fabricated of cast steel, which has a comparatively high coefficient of expansion. When the low expansion components are contained mechanically by the steel gooseneck structure, therefore, the result is usually distortion, breakage, and/or misalignment of the shot cylinder in the gooseneck seat.

Because of these problems, the usual procedure is to tighten the various parts of a hot chamber machine while they are at the operating temperature level and to loosen the parts before the machine is cooled to room temperature at the end of a production period. In the practice of the present invention, as explained in more detail hereinafter, any minor difference in thermal expansion which occurs between the shot cylinder and gooseneck structure is automatically compensated for by hydraulic cylinders associated with the shot cylinder.

SUMMARY OF THE INVENTION Broadly, the invention provides a hot chamber die casting machine which includes a melting pot having a gooseneck. Molten metal to be die cast is contained in the melting pot and the metal injection end of the gooseneck defines a seat portion in which the wall surface tapers inwardly and downwardly to a bore in the gooseneck. The lower end of the shot cylinder engages the tapered gooseneck seat and the shot cylinder is vertically aligned in the gooseneck seat by a means which engages the upper end ofthe cylinder. The metal shot is made by a slidable piston in the shot cylinder which is adapted to force molten metal out of the cylinder'into the gooseneck bore. The shot piston is also vertically aligned in the shot cylinder by another alignment means which engages the cylinder alignment means and the piston itself. A third means is provided which engages and presses downwardly on the cylinder align ment means to force the cylinder down into sealing contact with the gooseneck seat while the shot is being made. At the end ofa production period, the lower end of the shot cylinder is disengaged from the gooseneck seat.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a side elevation view ofa hot chamber metal die casting machine which incorporates the shot cylinder alignment and seating apparatus of this invention.

FIG. 2 is an enlarged fragmentary view of one embodiment of the shot cylinder-gooseneck bore seat connection as shown in the apparatus of FIG. 1.

FIG. 3 is an enlarged fragmentary view of a shot cylinder-gooseneck bore seat connection which is an alternative embodiment to that shown in FIG. 2.

DESCRIPTION OF A PREFERRED EMBODIMENT In the drawing, referring particularly to FIG. 1, the numeral 10 designates generally a hot chamber metal die casting machine. The molten metal to be die cast, as indicated by numeral 11, is contained in a cast steel melting pot 12. One side of the melting pot 12 defines a gooseneck portion 13 having a central bore 14 therein. The lower end of the gooseneck bore 14, i.e., the metal injection end, defines a seat 15 which is in direct communication with the bottom of the melting pct 12. Specifically, the gooseneck seat 15 is defined by a wall surface 16 which tapers inwardly and downwardly from the bottom of the melting pot 12 to join into the gooseneck bore 14. The angle of taper of wall surface 16 is preferably from about 15 to 30 from the vertical axis of the bore. v

The upper end of gooseneck bore 14, i.e., the outlet end, is in communication with a die assembly (not shown). To make a metal shot, a shot cylinder 17 is gagement of a radial lip 18, which is defined at the I periphery of the lower end of shot cylinder 17, with the tapered wall surface 16 of gooseneck seat 15. In the practice ofthe invention it is essential to achieve a positive seal" at the point of contact of radial lip 18 with the gooseneck seat 15. Specifically, this scal" connection must be sufficiently positive to withstand the high internal pressure created by the molten metal as the metal is forced downwardly into the gooseneck seat by piston 19 when the "shot" is made. Unless a positive seal is achieved, therefore, the high pressure exerted by the metal against the lower end of the shot cylinder will force the shot cylinder upwardly so that it breaks contact with the gooseneck seat. If this happens a substantial amount of the molten metal in the gooseneck seat will bypass through the resulting gap and destroy the integrity of the shot".

During the shot-making operation, the positive seal connection of radial lip 18 with gooseneck seat 15 is maintained by applying a continuous downward force against the upper end of shot cylinder 17. Shot cylinder 17 also includes an annular rib 18a, which is defined at the lower end of the cylinder bore. The purpose of rib 18a is to reinforce the lower end of shot cylinder 17 to prevent the cylinder end from being distorted or broken during the shot-making operation. In other words, in seating of radial lip 18 against the tapered wall surface 16 of gooseneck seat 15, only a thin, single line of contact is established at the shot cylindergooseneck seat. Although the small contact area provides a good molten metal sea] at the seat connection, the high temperature of the molten metal environment, combined with high inward pressure against the cylinder wall, is sufficient to distort the cylinder bore or break the cylinder end.

Another solution to the problem of distorting or breaking the lower end of the shot cylinder is provided by the embodiment illustrated in FIG. 3. Referring to FIG. 3, the gooseneck seat is identical in construction to the gooseneck seat of FIG. 2, i.e., the wall surface 16 tapers at an angle offrom about 15 to 30 from the vertical axis of the gooseneck bore. The lower end ofa shot cylinder 33 is seated down into gooseneck seat 15, with the actual seat connection being formed by engagement of a peripheral lip 34 with the tapered wall surface 16. Lip 34 is constructed with the same taper angle, i.e., 15 to 30, as the wall surface 16. The matching fit of lip 34 to wall surface 16 distributes the force applied to shot cylinder 33 over a fairly large area and enables the lower end of the cylinder to absorb the load without distorting or breaking.

Several co-acting members are required to properly align and seat the shot cylinder in the gooseneck bore and to align the shot piston in the cylinder. The shot cylinder alignment means is provided by a sleeve 20 and a flange 21. the lower end of sleeve 20 defines an annular shoulder 20a, which is shrinkfitted onto the upper end of shot cylinder 17. Flange 21, which is positioned above sleeve 20, fits down into an opening in lid 12a of melting pot 12. The lower face of flange 21 defines a hub 21a, which fits down into a counterbore 20b at the upper end of sleeve 20. Positioned above flange 21 is a stuffing box 22, which encloses stem 19a of piston 19. A lower shoulder 22a on stuffing box 22 seats down against a corresponding shoulder 21b, as defined by a counterbore in the upper face of flange 21. Fitted into stuffing box 22 is a bearing 23, which engages piston stem 19a. The combined function of stuffing box 22 and bearing 23 is to keep piston 19 vertically aligned in shot cylinder 17 during up-and-down movement of the piston in the shot-making operation.

To positively seat" the shot cylinder 17 in gooseneck seat 15 requires several members which comprise a hold-down assembly. Means for pushing flange 21 downwardly against sleeve 20 are provided by hold-down rods 24, 25. The lower end of each rod seats into a counterbore on the upper face of flange 21 adjacent to flange shoulder 21b. The upper end of each hold-down rod fastens into the bottom side of a horizontally disposed bar, which defines a hold-down crosshead 26. Positioned above and parallel with the crosshead bar 26 is a stationary support bar 27. Bar 27 is an upper cross member of a conventional A-frame support (the upright members are not shown).

A hydraulic cylinder 28, having a slidable piston 28a therein, is mounted at one end of support bar 27. An identical hydraulic cylinder 29, which includes slidable piston 29a, is mounted at the opposite end of bar 27. The stems of pistons 28a and 29a are bolted into the top side of cross-head bar 26, so that on the down stroke of each piston the cross-head bar 26 is pushed downwardly. Mounted on the top side of support bar 27 is a hydraulic oil cylinder 30. Oil cylinder 30 contains a main piston (not shown) which provides the power for operating the shot piston 19. A stem 31 of the main piston is connected to the shot piston stern 190 by a two-part, lockable coupling member 32.

The shot cylinder alignment and seating apparatus of this invention is particularly suitable for hot chamber die casting of the common light metals, such as magnesium, aluminum and zinc alloys. Shot cylinders 17 and 33 and the alignment sleeve 20 must be fabricated of materials which will resist the high temperatures of the molten metal environment and chemical attack from the aluminum constituent in the magnesium and aluminum alloys. Suitable materials include refractory metals and metal alloys, such as molybdenum, niobium, tantalum and tungsten, and various metal borides and carbides, such as titanium diboride, tungsten carbide and the like. A preferred material is a molybdenumbased alloy.

An additional problem, which is encountered particularly in the die casting of magnesium alloys, is abrasive wear of the gooseneck seat 15. Over a period of time the gooseneck seat will be abraded by small particles of extremely hard, nonmetallic materials, such as magnesium oxides and nitrides, which become wedged between the radial lip 18 on shot cylinder 17 and the wall surface 16 of gooseneck seat 15. In practice, therefore, it is preferred to insert an abrasion-resistant liner (not shown) in the gooseneck seat 15. Preferred liner materials are high temperature grade, wear-resistant metal compositions, such as alloys comprising a mixture ofcobalt, chromium and tungsten.

To illustrate the practice of the invention, the present apparatus is described as it would function in a typical magnesium alloy die casting operation. Referring particularly to FIG. 1, theshot piston 19 is moved up and down in shot cylinder 17 by the main piston in hydraulic oil cylinder 30. On the upstroke of piston 19,

' the molten metal 11 in melting pot l2 flows into cylinder 17 through a series of portholes in the cylinder, as indicated in 17a. The actual metal shot" is made on the downstroke of piston 19, which forces the liquid metal out of cylinder 17 and upwardly through gooseneck bore 14 into a die mold (not shown) in communication with the bore. The path of the metal is indicated by the arrows in the drawing.

Before and during the downward travel of piston 19 in shot cylinder 17, to make the shot, the lower end of the cylinder is wedged down into the gooseneck seat 15 by the action of the various members of the holddown assembly. Referring first to hydraulic cylinders 28 and 29, the flow of hydraulic fluid (not shown) into the upper part of each cylinder pushes the pistons 28a and 29a downwardly. The downward movement of pistons 28a and 29a pushes cross bar 26 downwardly. ln sequence, the downward force on the cross bar 26 is transmitted through hold-down rods 24 and 25, flange 21, and sleeve 20, and thence down against the upper end of shot cylinder 17. To achieve the desired positive seal" at the shot cylinder-gooseneck seat, the hydraulic fluid pressure directed against the heads of the pistons 28a and 29a is maintained at a constant pressure. The actual fluid pressure in cylinders 28 and 29 is maintained at the required constant level by adjust ment of a relief valve (not shown) positioned in a line (not shown) which controls the maximum pressure. In addition, the fluid pressure is sensed by a pressure switch not shown) positioned in the line. If the pressure should be insufficient to hold the shot cylinder 17 in sealing contact with gooseneck seat 15, the pressure switch immediately stops the shot" sequence.

In the shot making" operation the amount of force applied to the top of the shot cylinder must be enough to resist any upward forces on the shot cylinder and, at the same time, to keep the lower end of the shot cylinder in sealing contact with the gooseneck seat. One of the upward forces acting on the shot cylinder is created by the fluid metal pressure against any exposed portion of the lower end of the shot cylinder. Another upward force can occur when the shot piston 19 sticks in shot cylinder 17, for various reasons, at the same time that the system is attempting to return the piston to its normal raised position.

At the end of a production period, usually about one week, the shot cylinder 17 is disengaged from gooseneck seat before the metal is allowed to freeze. This prevents damage to the shot cylinder as the steel gooseneck structure contracts during the cool-down period. The shot cylinder is disengaged from the gooseneck seat by a manual operation which involves pushing a button (not shown) which controls the operation ofthe hold-down assembly.

What istclaimed is:

l. In a hot chamber metal die casting machine, which includes a melting pot with a gooseneck therein, the combination of:

a. a gooseneck seat positioned at the metal injection end of the gooseneck, the seat being defined by a wall surface which tapers inwardly and downwardly to a bore in the gooseneck;

b. a shot cylinder which has an upper and lower end, the lower end being adapted to engage the tapered wall surface of the gooseneck seat;

c. a means which vertically aligns the shot cylinder in the gooseneck seat, the said cylinder alignment means including a sleeve member which has an upper and lower end, the lower end engaging the upper end of the shot cylinder, and a flange member which has an upper and lower face, the lower face engaging the upper end of the sleeve member;

d. a slidable piston in the shot cylinder which is adapted to force molten metal out of the shot cylinder into the gooseneck bore to make a metal shot;

e. a means which vertically aligns the piston in the shot cylinder, the said piston alignment means including a stufflng box which seats against the upper face of the flange member and which encloses the slidable piston, and a bearing member which fits into the stuffing box and which engages the slidable piston; f. a means for holding down the shot cylinder to obtain sealing contact of the shot cylinder with the gooseneck seat while the metal shot is being made, the said shot cylinder hold-down means including at least two rod members which each have an upper and lower end, the lower end of each rod member engaging the upper face of the flange member, a cross bar member which has a top side and a bottom side, the bottom side engaging the upper end of each rod member, and at least two piston members, each piston member being attached to opposite ends of the top side of the cross bar member.

2. The machine of claim 1 which includes means for disengaging the lower end of the shot cylinder from the gooseneck seat before the metal is allowed to freeze at the end of the production period.

3. The machine of claim 1 wherein the gooseneck seat and the shot cylinder are each constructed of a different material and the shot cylinder material hasa substantially lower coefficient of thermal expansion than the gooseneck seat material.

4. The machine of claim 1 in which the wall surface of the gooseneck seat tapers inwardly and downwardly at an angle of from about 15 to 30.

5. The machine of claim 1 in which the lower end of the shot cylinder includes an annular rib on the cylinder bore and a radial lip on the periphery of the cylinder.

6. The machine of claim 1 in which the lower end .of the shot cylinder includes a peripheral lip which tapers inwardly and downwardly at an angle of from about 15 to 30.

7. The machine of claim 1 in which the bers are hydraulically operated pistons.

piston mem- 

1. In a hot chamber metal die casting machine, which includes a melting pot with a gooseneck therein, the combination of: a. a gooseneck seat positioned at the metal injection end of the gooseneck, the seat being defined by a wall surface which tapers inwardly and downwardly to a bore in the gooseneck; b. a shot cylinder which has an upper and lower end, the lower end being adapted to engage the tapered wall surface of the gooseneck seat; c. a means which vertically aligns the shot cylinder in the gooseneck seat, the said cylinder alignment means including a sleeve member which has an upper and lower end, the lower end engaging the upper end of the shot cylinder, and a flange member which has an upper and lower face, the lower face engaging the upper end of the sleeve member; d. a slidable piston in the shot cylinder which is adapted to force molten metal out of the shot cylinder into the gooseneck bore to make a metal shot; e. a means which vertically aligns the piston in the shot cylinder, the said piston alignment means including a stuffing box which seats against the upper face of the flange member and which encloses the slidable piston, and a bearing member which fits into the stuffing box and which engages the slidable piston; f. a means for holding down the shot cylinder to obtain sealing contact of the shot cylinder with the gooseneck seat while the metal shot is being made, the said shot cylinder hold-down means including at least two rod members which each have an upper and lower end, the lower end of each rod member engaging the upper face of the flange member, a cross bar member which has a top side and a bottom side, the bottom side engaging the upper end of each rod member, and at least two piston members, each piston member being attached to opposite ends of the top side of the cross bar member.
 2. The machine of claim 1 which includes means for disengaging the lower end of the shot cylinder from the gooseneck seat before the metal is allowed to freeze at the end of the production period.
 3. The machine of claim 1 wherein the gooseneck seat and the shot cylinder are each constructed of a different material and the shot cylinder material has a substantially lower coefficient of thermal expansion than the gooseneck seat material.
 4. The machine of claim 1 in which the wall surface of the gooseneck seat tapers inwardly and downwardly at an angle of from about 15* to 30*.
 5. The machine of claim 1 in which the lower end of the shot cylinder includes an annular rib on the cylinder bore and a radial lip on the periphery of the cylinder.
 6. The machine of claim 1 in which the lower end of the shot cylinder includes a peripheral lip which tapers inwardly and downwardly at an angle of from about 15* to 30*.
 7. The machine of claim 1 in which the piston members are hydraulically operated pistons. 